1. Field of the Invention
The present invention relates to a variable dispersion compensation equipment, an optical transmission system using it, and a method of setting dispersion compensation quantity, and more particularly to a variable dispersion compensation equipment using an optical switch and a controller, an optical transmission system using it, and a method of setting the dispersion compensation quantity therein.
2. Description of Related Art
Loss compensation technology using optical amplifiers, dispersion compensation technology using dispersion compensating fibers and other dispersion compensators, the increased transmission speed, adaptation of optical amplifiers to wider bands and the increased density of wavelength multiplexing have worked together to make possible large-capacity transmission over a long distance.
According to U.S. Pat. No. 5,838,867, cascade connection of dispersion compensating fibers and fibers to be compensated in an appropriate length ratio is claimed to enable wavelength dispersion over the whole system including the dispersion compensating fibers to be improved in the 1.55 μm (micrometer) wavelength band.
U.S. Pat. No. 5,608,562 discloses a variable dispersion compensation equipment combining a three-port optical circulator, plural 2×2 optical switches, plural dispersion compensating fibers and a mirror.
In Japanese Laid-Open Patent Publication No. 2004-193974, an optical cross-connecting equipment which performs variable dispersion compensation as required is described, but no mention is found of the means of variable dispersion compensation.
As the dispersion compensator for use in an optical communication system, it is the usual practice to use what has a fixed dispersion compensation quantity, such as the dispersion compensating fibers disclosed in U.S. Pat. No. 5,838,867. However, since the dispersion compensation quantity necessary for an optical communication system depends on the type and the length of optical fibers constituting a network, these items of information should be obtained beforehand when a dispersion compensator is to be designed and fabricated, and if no sufficient information is available, the wavelength dispersion of the optical fibers to be actually used needs to be measured before the designing and fabrication.
If these items of information are acquired only immediately before the introduction of the system, the process of designing and fabricating the dispersion compensator may affect the start-up timing of the system operation.
Further, where the dispersion compensation quantity of the dispersion compensator is fixed, if the dispersion compensation quantity is varied finely to enhance the accuracy of dispersion compensation, many different types of dispersion compensators will be needed, causing a problem of complex management.
If the optical fiber length is to be altered on account of trouble or relocation, the dispersion compensation quantity should be altered accordingly, and the dispersion compensators should be replaced to match the changed quantity. Since this replacement is a manual operation entailing the disengagement and reengagement of optical connectors, the optical communication line cannot be used for a few seconds or even dozens of seconds.